Borna disease virus (BDV) is an enveloped virus with a non-segmented negative strand (NNS) RNA genome. Because of its unique features BDV is the prototypic member of a new virus family. BDV is highly neurotropic and is an important model system for the study of CMS viral persistence. BDV entry into host cells is mediated by specific interactions of the BDV surface glycoprotein (G) with so far unidentified cellular receptor proteins. Studies about BDV-receptor interactions have been impeded by an extreme paucity of infectious virions. We have generated a recombinant VSV (rVSV.G*/p56) where the BDV G was substituted for the VSV G. Notably, rVSV.G*/ p56 recreates the cell tropism and entry pathway of BDV, and grows to high titers. Using this novel tool we can now implement new strategies by which to identify BDV cellular receptors. Our specific aims are: 1. Identify BDV candidate cellular receptor proteins. We will use genetic and biochemical approaches. The genetic approach will involve genetic complementation of receptor-null cell lines with cDNA libraries generated from cells and tissues that are highly susceptible to BDV. Complemented cells expressing candidate receptor proteins will be identified by their susceptibility to rVSV.G*/p56, or BDV G-retroviral pseudotypes. The biochemical approach will be based on the use of: (i) a virus overlay protein blot assay (VOPBA), and (ii) BDV G immunoadhesins to select cell surface proteins that specifically interact with BDV G. In both cases protein identities will be determined using MS procedures. 2. Functional validation of BDV candidate cellular receptor proteins. For this we will use the following approaches: 1) transfection of BDV receptor-null cells with the candidate cDNA should confer susceptibility to rVSV.G*/p56; 2) RNAi-mediated knock-down expression of candidate receptors in BDV susceptible cells should confer cells with increased resistance to both BDV and rVSV.G*/p56; 3) Determination of expression pattern of BDV candidate receptors in vivo.